One of the biggest problems with gulpers appears to be that they fall ill and die often early on or after some months, maybe a year. I don't recall a single report of anyone keeping them for a long time, for at least 5-10 years.
But this could be because people start threads and ask questions only when there is a problem - these threads abound. Some report problems immediately, which I think have to do with water - gulpers are not very adaptable, they come from soft, low TDS, acidic, black water.
Others report problems within the first year, which I think may have to do also with the water (not as drastically different from their preferred water) but also perhaps with the diet.
All in all, it would appear gulpers are problematic, sensitive, not a starter fish.